sigma

The 18th letter of the Greek alphabet.

A sigma factor.

The standard deviation of a given probability distribution or a given set of data.

The curve of the letter S or any approximate curve.

In descriptive biol., one of the S-shaped ridges on the surface of certain molluscan shells, as those of gastropods and cephalopods.

In experimental psychology, the time-unit, of a second: abbreviated σ.

The name of the Greek letter Σ, σ, ς, equivalent to the English S, s. (For its early forms, see under S.)

An S-shaped or sigmoid flesh-spicule of a sponge.

The Greek letter Σ, σ, or ς (English S, or s). It originally had the form of the English C.

The name for the eighteenth letter of the Classical and Modern Greek, the nineteenth letter of Old and Ancient.